Revisiting Late Quaternary chronostratigraphy of the Arctic Ocean using the 230Th excess method

The Late Quaternary chronostratigraphic framework of the Arctic Ocean remains contentious, hindering our understanding of Arctic paleoceanographic conditions and their influence on global climate change. Recent advances in microbiostratigraphy and amino acid racemization (AAR) dating challenge the high-sedimentation rate central Arctic scenario proposed nearly two decades ago. To address this issue, U-Th analyses were performed on a Lomonosov Ridge sediment core, ICE04, whose chronostratigraphy had previously been established using AMS¹⁴C dating, lithological and mineralogical correlations, and the identification of a paleomagnetic excursion.

The Th-230 excess (²³⁰Th_xs) distribution and decay downcore suggest a revised age framework. Specifically, the previously identified marine isotope stage (MIS) 3 layer can be re-assigned to MIS 3 to 6, while the MIS 4/4-5d layer extends back to MIS 7. Additionally, the ²³⁴U/²³⁸U ratio record indicates active late diagenetic processes likely driven by organic carbon decomposition. These findings highlight several key points: 1) younger organic carbon may dissolve and reprecipitate downcore due to late diagenetic processes, limiting the reliability of ¹⁴C ages derived from bulk organic carbon; 2) lithological correlations used to construct Late Quaternary chronostratigraphy can introduce significant uncertainties and may be biased by the misinterpretation of other methods, such as ¹⁴C dating; 3) dolomite peaks are recommended as reliable markers for the site-to-site correlations as they are linked to the meltwater discharge from the NW margin of the Laurentide Ice Sheet; and 4) the 1-meter-thick interval exhibiting a negative geomagnetic polarity, previously attributed to the Matuyama Chron (~780 ka) or the Laschamp (~41 ka) and Mono Lake (~35 ka) excursions, is dated to MIS 4-5d using the ²³⁰Th_xs method. The revised age addresses the complexity of paleomagnetic behavior in the Arctic and underscores the need for further investigation to resolve these discrepancies.

Using the ²³⁰Th_xs method, we estimate a late Quaternary mean sedimentation rate of <2 cm/ka for core ICE04, significantly lower than the previously reported rate of >4 cm/ka. These findings align with the sediment-starved deep Arctic scenario proposed prior to the 2000s, further indicating that an effort must be conducted to account for all the available data.